1. Field of the Invention
This invention relates to thermally-responsive record material. In particular this invention relates to such record material in the form of sheets coated with color-forming systems comprising chromogenic material and acidic color developer material. More particularly, this invention relates to record material having improved resistance to fingerprinting and smearing upon being handled.
2. Description of the Invention
Thermally-responsive record material system are well known in the art and are described in many patents, for example U.S. Pat. Nos. 3,539,375; 3,674,535; 3,746,675; 4,151,748; 4,181,771; 4,246,318 and 4,470,057 incorporated herein by reference. In these systems, basic chromogenic material and acidic developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit said materials to react, thereby producing a colored mark.
Thermally-responsive record materials have been progressively improved in sensitivity over the years in keeping with the requirements imposed by faster and faster facsimile equipment transmission and operating rates. High sensitivity thermal paper must promptly and efficiently form a high density mark upon thermal heating. As sensitivities have increased with the use of thermal modifiers, a vexing problem has emerged with high sensitivity thermal papers of image erasure and smearing from fingerprint oils upon being handled following image formation. A need has arisen with high sensitivity thermal papers for coated composition which resist image erasure due to fingerprint oils.
U.S. Pat. No. 4,134,847 to Oda et al. disclosed a developer composition comprising an aromatic carboxylic acid and oxide or carbonate of a polyvalent metal and including a polymeric material such as poly .alpha.-methylstyrene.
U.S. Pat. No. 4,470,057 to Glanz disclosed thermally-responsive record materials which can include a latex binder such as polystyrene latex to protect the coated materials from brushing and handling forces.
None of the prior art recognized the superior resistance to image erasure due to fingerprint oils achieveable with a coating containing poly-.alpha.-methylstyrene or .alpha.-methylstyrene-vinyltoluene copolymer in combination with a thermal modifier such as acetoacet-o-toluidine, diphenoxyethane, phenyl-1-hydroxy-2-naphthoate, diheptadecyl ketone, or octadecanamide.
It is an object of the present invention to provide a thermally-responsive record material which resists smearing and/or image erasure upon contact with fingerprint oils and commonly used lotions.